Generation 2 nuclear reactors This refers to the class of commercial reactors built up to the end of the 1990s. These are Boiling Water Reactors, (BWRs) as at Fukushima Dai-ichipower plant. They are in operation today at many other places, at least 23, and probably more, in USA.

(above Vermont Yankee nuclear reactor) Generation II reactor designs generally had an original design life of 30 or 40 years. However many generation II reactor are being life-extended to 50 or 60 years, and even to 80 years, despite serious safety doubts!

Generation 3 nuclear reactors

Advanced Boiling Water Reactor (ABWR) — A GE design that first went online in Japan in 1996.
Advanced Pressurized Water Reactor (APWR) — developed by Mitsubishi Heavy Industries.
Enhanced CANDU 6 (EC6) — developed by Atomic Energy of Canada Limited.
VVER-1000/392 (PWR) — in various modifications into AES-91 and AES-92

Advanced Heavy Water Reactor being developed by BARC,India to utilize Thorium.
The reactors operate at relatively low temperatures, leaving the bulk of the fuel unburned as waste. In fact, only less than 1% of the fuel is converted into useful energy. This creates an enormous amount of radioactive nuclear waste. In particular, some of the transuranic elements produced by the process have enormously long half-lives.

Generation IV nuclear reactors. Unlike Gen III+, which evolved from existing Pressurized Water Reactors (PWRs) and Boiling Water Reactors (BWRs), these would be based on radical new technologies. Six technologies were selected by the major nuclear countries as the most promising.

However, 10 years on, they seem no closer to commercial deployment. These designs were a mix of designs already pursued, such as sodium-cooled fast reactors and helium/graphite high-temperature reactors, and totally untested options such a lead-cooled fast reactors. The more familiar reactors have a very poor record so far, despite all major nuclear nations trying to develop them over the past 50 years. Demonstration fast reactors like Superphenix, Monju and Dounreay, and high-temperature reactors like THTR-300 and Fort St. Vrain had highly problematic, often short lives. http://www.theenergyreport.com/pub/na/12441

Generation 1V nuclear reactors are in general “fast breeder” reactors, designed to produce more nuclear fuel than they consume.

Nuclear reprocessing separates plutonium from the used nuclear fuel. Originally this was done to get plutonium for nuclear bombs. More recently, reprocessing has become part of the technology for breeder reactors.

However, these reactors designed to use plutonium wastes in Mixed Oxide Fuel (MOX) have turned out to be an environmental and economic disaster, for example at Sellafield in England, and at Monju in Japan.

Small Modular Reactors (SMR’s) Small Modular Reactors, [SMRs] the latest “rabbit out the nuclear hat,” are generally based on scaled down BWR or PWR technology and illustrate the nuclear industry’s schizophrenic attitude to reactor size…. it was clear that the AP600 [small nuclear reactor] was hopelessly uneconomic… SMRs may turn out to be the latest in a long line of nuclear designs that looked good on paper, but could not make the transition to commercial technology

Westinghouse AP 1000 it was clear that the AP600 was hopelessly uneconomic, so Westinghouse nearly doubled its output in the AP1000, which received final regulatory approval in December 2011. The AP1000 is still proving far too expensive and China is now examining the possibility of scaling it up to 1,800 MWh to reduce cost.

Integral fast Reactors Generation IV reactor designs are largely Fast Neutron Reactors, that can consume nuclear waste through fission. Since the 1950s, roughly $100 billion has been spent on the research and development of such reactors around the world, yet there is currently only one producing electricity—the BN-600 reactor in Russia, operational since 1980…..

The most prevalent type operate at temperatures as high as 550 degrees Celsius and use liquid sodium instead of water as a coolant. Sodium burns explosively when exposed to either air or water, necessitating elaborate safety controls…..

But attempts to make that technology commercial have largely failed, mostly because of difficulties with controlling sodium fires and the steam generators that transfer heat from the sodium to water.

These reactors require that the spent nuclear fuel be reprocessed, a technical program that involves extracting plutonium and other fissile materials from the depleted uranium fuel rods. Of course, such plutonium and highly enriched uranium are also exactly the isotopes used to make nuclear weapons, making the materials security threats. Fast reactors cost substantially more than light-water reactors…[and]…that, relative to thermal reactors, they’re not very reliable …. And at the end of it all there is still the need for a permanent repository for the nuclear wastes.http://www.scientificamerican.com/article.cfm?id=are-new-types-of-reactors-needed-for-nuclear-renaissance

Thorium reactors. – such as Liquid Fluoride Thorium Reactor (LFTR) In this reactor, because thorium is not a fissile material, you actually need either plutonium or enriched uranium to start it. With this particular reactor, most people will want a reprocessing, that is separating the fissile material on-site. so you have a continuous flow of molten salt out of the reactor. You take out the protactinium-233, which is a precursor of uranium, and then you put the uranium back in the reactor, and then you keep it going. Thorium reactors still create highly radioactive wastes – Cesium-137 and strontium-190, hundreds of years, just like today’s reactors. Cesium-135 and iodine-129, millions of years half-life. Technetium-99, 200,000 years. – Dr. Arjun Makhijani

Uranium 233 is fissionable, and you can make bombs out of it. And the best part of all is that it can be purified chemically out of the spent fuel of the thorium reactor. You don’t have to mess around with gas diffusion or centrifuges.

1.This Month

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Changing climate change“2040” paints an optimistic picture of the future of the environment

The film focuses on technological and agricultural solutions that are already being implemented to help combat climate change, The Economist Feb 19th 2019

by C.G. | BERLIN ……….In “2040”, a documentary which premiered at the Berlinale, Mr Gameau seeks to wrest hope from the bleak reports of climate change. He was inspired by Project Drawdown, the first comprehensive plan to reverse global warming, and the film is intended as a “virtual letter to his four-year-old daughter to show her an alternative future”. “Many films,” Mr Gameau thinks, are too dystopian, and “paint a future that is really hard to engage and to connect with”. “2040” acknowledges that the Earth has set off down a hazardous path, but focuses on the work that is being done now to steer the right course. What, the film asks, could make 2040 a time worth living in?…. (subscribers only) https://www.economist.com/prospero/2019/02/19/2040-paints-an-optimistic-picture-of-the-future-of-the-environment